A tip I found recently advises you to aim to draw a full hand from your draw pile. Specifically, "11 cards isn't a good number to have." The article partially explains this, but I think it's worth working through in more detail to see why this is true and what this means.
The problem is that you can't shuffle what's not in the discard pile, and you want to exhaust and shuffle your entire deck at once. If you don't shuffle your entire deck at once, then there are some cards left over from your first run through the deck. Those leftover cards cannot possibly be drawn again until you completely exhaust your new draw pile! In fact, you aren't guaranteed to see these leftover cards again until you exhaust your draw pile twice. That could be a long time! For a 15-card deck, that's 6 turns.
Suppose you have 11 cards, as in their example. I made a visualization for this in Figure 1. You draw five cards the first two turns (shown in brownish red), leaving one left in the draw pile, shown in black. For concreteness' sake, let's say that card is Dexterity. When you draw on turn 3, you draw Dexterity, emptying your draw pile. But you still need to draw 4 more, so you must shuffle the discard pile of 10 cards to get a new draw pile of 10 (shown in green), and draw 4 of those, leaving 6. You end your turn without using Dexterity and it ends up in the discard.
Now because of the odd draw pile size, you won't be drawing Dexterity again until you go through the 6 cards in your draw pile. The earliest you can draw it is turn 5, when you reshuffle the discard pile that Dexterity is in to get the new draw pile (shown in sky blue). You aren't guaranteed to draw Dexterity until turn 7.
This is unlike what happens with the first-drawpile cards drawn on 1 and 2. These are shown in red before the shuffle and green after the shuffle. As you can see, they are all guaranteed to be drawn by turn 5.
Because this example deck is small the delay is relatively small. With larger decks the delay gets worse. This problem is worse if you are unlucky enough to end up drawing a critical setup card from the bottom of your deck... like Dexterity.
So what does this mean?
In theory, as they say, it means you should try to make your deck size a multiple of the number of cards you draw per turn. But in practice things get complicated, because a bunch of cards offer you card draw. You can adjust for that by adding up the number of extra cards drawn over all your cards and subtracting this total from your deck size for "multiple checking" purposes. However, this isn't quite right either because it assumes you'll always use those cards when they come up. In practice you might or might not play those cards on a given run through the deck. Also Silent's starter artifact, the Ring of the Snake, gives you +2 card draw the first turn, which just screws things up worse. So in practice, I'm not sure it makes sense to worry about deck size.
It might does make sense to account for this drawing thing, though, in some critical fights e.g. vs. a dangerous elite or a boss. It probably makes sense, if you are nearing the end of the deck and have draw cards, to check what's in your draw pile – in particular because this seems to be a useful thing to do anyway. If you can empty your draw pile without going over, or if you can fetch a critical card without hitting the bottom of the pile, that will keep it from cycling "too late" and ending up like our poor Dexterity card in the example.